How Is U.S. Duty Calculated When You Import Custom CNC Machining Parts From China?

We process hundreds of CNC part shipments to the US every year, and the single question we hear most from new clients is: "What will my total duty actually be?" It is never one number — and that gap between expectation and reality has caused real budget overruns.

U.S. duty on CNC machined parts from China is a stack of six separate charges, all calculated on the same customs value. The full formula in 2026 is: base MFN duty + Section 301 tariff + Section 232 metals tariff + IEEPA baseline tariff + Merchandise Processing Fee + Harbor Maintenance Fee. For metal-heavy precision parts, this stack routinely reaches 45–70% of CIF value.

Understanding each layer is not optional for a purchasing manager. It is the only way to build an accurate landed cost and compare suppliers fairly.

How Do I Find the Correct HTS Code for My CNC Parts?

Getting the HTS code wrong is one of the most expensive mistakes we see clients make. The 10-digit code drives nearly every number in your duty calculation — and CBP will not forgive a careless guess.

The correct HTS code for CNC machined parts is the 10-digit number that matches the part's material, function, and end-use classification. It controls the base MFN duty rate, whether Section 301 applies, and access to active USTR exclusions. There is no shortcut — each part family must be classified individually using the current USHTS schedule.

Why the 10-Digit Code Is the Most Important Input in Your Duty Calculation

The Harmonized Tariff Schedule of the United States ¹ (USHTS) organizes goods into chapters by material and function. For CNC machined parts, most classifications fall in Chapter 73 (articles of iron or steel), Chapter 76 (aluminum articles), or Chapter 84 (machinery parts). Within each chapter, the 10-digit code narrows down to the specific article type.

Here is why precision matters:

How to Find the Right Code

Start with the USITC DataWeb portal (dataweb.usitc.gov). Search by material and product description. Then cross-reference with the CBP Rulings Database ² to find binding rulings issued for similar parts. If your part is borderline between two headings, a binding ruling request to CBP is the safest path — it takes roughly 30 days and gives you legal certainty.

Never rely on the code your Chinese supplier puts on the commercial invoice. Suppliers sometimes use codes that minimize their own export compliance burden, which may not match the correct US import classification.

What Happens After You Have the Code

Once you have the 10-digit code, three lookups follow immediately:

1. MFN duty rate — Look up the General rate of duty in Column 1 of the current USHTS schedule.
2. Section 301 list assignment — Check the USTR Section 301 docket to see if your 8-digit subheading is on List 1/2/3 (7.5%) or List 4A (25%). Also check for active exclusions.
3. Section 232 coverage — Determine if your parts qualify as derivative articles under the April 2026 proclamation and whether foreign metal content exceeds 15% of total weight.

As of May 2025, the de minimis exemption for China-origin goods has been eliminated. Even a single prototype sample now requires a formal customs entry with a valid 10-digit HTS code. There are no shortcuts for low-value test orders.

Common Classification Mistakes

The most frequent error we encounter is classifying a machined aluminum housing under a general "parts of machinery" heading when it should be classified as an aluminum article. The difference can be 3 percentage points in MFN duty — and a completely different Section 301 list assignment.

A second common mistake is ignoring end-use. Some headings offer lower duty rates for parts used in specific industries, such as aviation or medical devices. Missing that option costs money on every shipment.

What Extra Tariffs Could Apply to Parts Made in China?

Beyond the base MFN duty, several additional tariff layers apply specifically to Chinese-origin goods. Each is calculated on the same customs value and added on top. Missing even one layer can turn a profitable import into a loss.

Extra tariffs on China-made CNC parts currently include Section 301 tariffs of 7.5% or 25%, a Section 232 metals tariff of 25% on the full customs value of derivative metal articles, and an IEEPA baseline tariff of 10%. In 2026, these three layers alone can add 42.5 to 60 percentage points on top of the base MFN duty rate.

Section 301 Tariffs: 7.5% or 25%

Section 301 tariffs ³ were imposed by the Office of the United States Trade Representative (USTR) starting in 2018 as a response to Chinese trade practices. They apply to a large share of Chinese-origin goods, organized into product lists.

USTR has extended 178 specific product exclusions through November 2026. If your exact HTS code appears on the active exclusion list, this entire tariff layer disappears. It is worth checking before every shipment because the list changes.

Section 232 Metals Tariffs: The April 2026 Restructuring

This is the layer that changed most dramatically in 2026. The old "unstacking" method — which let importers pay Section 232 only on the raw metal content of a finished part — has been eliminated.

Under the April 6, 2026 proclamation ⁴:

• Derivative articles (finished parts where foreign metal content exceeds 15% of total weight): 25% on the full customs value of the entire finished product.
• Primary metal mill products: 50% on the full customs value.

This restructuring significantly increased the effective Section 232 burden on precision CNC parts. A machined steel bracket previously calculated Section 232 only on the steel billet cost. Now it applies to the entire machined part value, including labor and overhead.

One additional risk: parts containing Russian-origin aluminum face a 200% Section 232 rate, regardless of where they were machined. Some Chinese suppliers source aluminum from multiple origins without disclosing the smelting country. Our team now requires explicit country-of-origin declarations for all metal inputs — especially aluminum — on every order. Clients should demand the same.

IEEPA Baseline Tariff: 10%

The International Emergency Economic Powers Act (IEEPA) ⁵ baseline tariff currently sits at 10% for China-origin goods. This rate reflects a paused reciprocal tariff that is scheduled for reassessment in November 2026 — at which point it could rise to 20% or higher.

This layer applies to essentially all Chinese-origin imports and must be included in every duty calculation. It is not optional and it is not negotiable.

Adding It All Together

For a typical CNC machined steel housing classified under a List 3 HTS code, the 2026 duty stack looks like this:

That 47% is calculated before broker fees, inland freight, and any warehousing costs. The landed cost is significantly higher than the FOB price alone.

Should I Confirm Duty Exposure Before I Approve the Supplier?

We always recommend running a full duty calculation before signing any purchase order. Many buyers lock in a price with a supplier and then discover the landed cost makes the project unprofitable. That sequence is painful and avoidable.

Yes, duty exposure must be confirmed before supplier approval. The customs value used as the duty base is CIF value — product cost plus international freight plus insurance. A $10,000 FOB shipment with $800 freight and $120 insurance has a $10,920 CIF customs value, meaning duties are calculated on a base 9.2% higher than the invoice price alone.

Why CIF Value Matters More Than FOB Price

Most buyers think in FOB terms because that is how suppliers quote. But US Customs calculates duty on CIF value — cost plus insurance plus freight — which is always higher. The difference compounds when duty rates are high.

Consider two shipments with the same FOB price but different shipping terms:

The routing decision alone adds $752 to the duty bill in this example. On larger shipments, the gap grows proportionally.

Building a Pre-Approval Duty Checklist

Before you approve a Chinese supplier for a CNC part order, work through these steps in order:

Step 1 — Classify the part. Identify the correct 10-digit HTS code. Do not accept the supplier's code without independent verification.

Step 2 — Look up all applicable duty rates. MFN rate, Section 301 list and rate (or exclusion), Section 232 applicability and rate, IEEPA baseline rate.

Step 3 — Get a freight estimate. Ask your freight forwarder for an estimated ocean freight and insurance cost for the expected shipment volume. Add these to the FOB price to get estimated CIF value.

Step 4 — Calculate MPF and HMF. The Merchandise Processing Fee ⁶ is 0.3464% of FOB value (min $33.58, max $651.50 per entry for FY2026). HMF is 0.125% of CIF for ocean shipments.

Step 5 — Total the landed cost. Add supplier FOB price + all duty layers + MPF + HMF + customs broker fee + inland delivery.

Step 6 — Confirm metal input origins. Ask the supplier to provide country-of-origin mill certificates for all metal inputs. Flag any aluminum that may be Russian-origin.

The Duty Drawback Consideration

If your business re-exports finished goods that incorporate imported parts, you may have previously used duty drawback ⁷ to reclaim duties paid on those parts. The April 2026 Section 232 proclamation significantly restricts this option.

Manufacturing drawback on Section 232 tariffs is now available only where the metal content was smelted or cast in a Trade Agreement Partner country — currently the UK, EU, Japan, South Korea, Mexico, and Canada. Chinese-smelted metal has no drawback eligibility. If your previous landed cost model assumed drawback recovery on re-exported assemblies, that model needs to be updated before you approve the next order.

How Can I Avoid Classification Mistakes That Increase Duty Risk?

Classification errors are not just paperwork problems. They trigger CBP penalties, delayed shipments, and sometimes retroactive duty bills covering years of imports. The good news is that most classification mistakes follow predictable patterns and can be prevented.

Avoiding classification mistakes requires three habits: always verify the 10-digit HTS code independently from your supplier, request a CBP binding ruling for any part where two headings could apply, and audit your active shipments whenever tariff proclamations change — especially after April 2026 Section 232 restructuring.

The Most Common Classification Errors for CNC Parts

After working with dozens of US importers, we have seen the same mistakes appear repeatedly. These are the ones that cost the most:

Confusing "parts of machinery" with material-based classification. Chapter 84 (machinery parts) and Chapter 73/76 (iron/steel/aluminum articles) overlap for many machined components. CBP's essential character test and use-at-importation rules determine which heading applies. Misclassifying a structural aluminum part as a "machine part" can understate the applicable Section 232 exposure.

Using a 6-digit international HS code instead of the full 10-digit US code. Many Chinese suppliers provide the 6-digit international code on commercial invoices. The 10-digit US code is not derivable from the 6-digit code without additional classification work.

Ignoring updates to tariff proclamations mid-year. The April 2026 Section 232 restructuring ⁸ changed how derivative articles are classified and rated. Importers who did not update their classifications after the proclamation may be filing under the wrong rate.

Practical Steps to Reduce Classification Risk

When to Involve a Licensed Customs Broker

For straightforward repeat parts, an experienced in-house team can handle classification. But for any of the following situations, bring in a licensed customs broker ⁹ (LCB) or customs attorney before filing:

• First import of a new part family
• Parts with mixed materials or complex assemblies
• Any part where Section 232 derivative article status is unclear
• Any part on or near the Section 301 List 4A boundary
• Re-importation of parts previously exported for processing

The cost of a broker consultation is almost always lower than the cost of a CBP penalty or a retroactive duty assessment.

Staying Current on Tariff Changes

Tariff policy for China has changed multiple times per year since 2018. The IEEPA baseline rate is scheduled for reassessment in November 2026. Section 301 exclusions ¹⁰ expire and are renewed on a rolling basis. Section 232 proclamations can be revised by executive order with limited notice.

The practical approach is to set a calendar reminder to audit active shipment classifications every time a major trade policy announcement is made. Waiting until CBP flags a problem is too late — the penalty clock starts at the time of entry, not the time of discovery.

Conclusion

U.S. duty on Chinese CNC parts is a stacked calculation, not a single number. Get the HTS code right, account for every tariff layer, and verify landed cost before you sign any purchase order. That discipline protects your margin on every shipment.

Footnotes

1. Search and browse the full US Harmonized Tariff Schedule by product description or HTS code. ↩︎
2. Search CBP's CROSS database for binding rulings on HTS classification of similar imported products. ↩︎
3. Official USTR page covering Section 301 China tariff actions, lists, rates, and active product exclusions. ↩︎
4. Perkins Coie analysis of the April 2026 Section 232 proclamation and its impact on derivative article valuation. ↩︎
5. CBP's official FAQ explaining IEEPA reciprocal tariff obligations and reporting codes for China-origin goods. ↩︎
6. CBP's official Merchandise Processing Fee rates, minimums, maximums, and exemptions for FY2026. ↩︎
7. CBP FAQ explaining Section 232 duty drawback eligibility rules following the April 2026 restructuring. ↩︎
8. GHY Trade Compliance guide to the April 2026 Section 232 restructuring and full customs value calculation. ↩︎
9. CBP's rulings and advance decisions portal for finding licensed customs brokers and requesting formal rulings. ↩︎
10. Great Lakes Customs Law tracker of Section 301 exclusion history, current active exclusions, and expiry dates. ↩︎